A common technique used to install heating, ventilation and air conditioning (HVAC) equipment, or other mechanical equipment for supporting building systems or processes, on a roof is to mount the equipment on a curb that rests on the surface of the roof. Generally, the section of roof that is framed by the curb is removed to allow ducts, pipes or electrical conduit to attach to the equipment. Using a curb is beneficial to installing the equipment directly on the roof surface for reasons such as avoiding damage to roofing materials, not blocking roof drainage paths, ensuring the equipment is above standing water or snow, and ensuring that the equipment is always mounted on a level surface.
A drawback of mounting HVAC equipment on the roof in the traditional raised roof curb configuration is that the equipment is highly susceptible to damage and deterioration caused by wind, rain, hail and other forces of nature. The cabinets of the equipment begin to deteriorate over time which can lead to leakage and reduced efficiency. Rooftop equipment is often considered unsightly by owners and architects, and consequently expensive screening is required to camouflage the equipment.
The construction of roof mounted HVAC equipment enclosures or cabinets is well known. A typical HVAC enclosure is illustrated by U.S. Pat. No. 4,118,083 issued to Lackey et al. It describes a cabinet (also commonly referred to as an equipment housing or equipment enclosure) surrounding piping, machinery, and electronics within. U.S. Pat. No. 4,139,052 to Lackey describes a conventional layout and construction of a contemporary roof top unit.
These HVAC equipment cabinets may be round (in the case of exhaust fans) or rectangular (in the case of air handling and self-contained roof top systems). There are often openings in the roof, floor and sidewalls of the cabinets to allow air to flow in or out of the unit and also allow connections to the unit's internal piping and electrical circuitry. Generally, physical access to the internal components is provided by hinged or removable doors in the sidewalls of the cabinet.
Improvements to the basic configuration of roof top mounted mechanical equipment have taken many forms. One such example for stand-alone refrigeration systems and enclosures is illustrated by U.S. Pat. No. 6,401,477 to Dubé. This patent describes a means to improve accessibility to the equipment inside the cabinet for maintenance purposes.
Due to the desire to keep these cabinets light weight and low in cost, they are often formed from light gage metal. Unfortunately, this metal is easily damaged by high winds or hail. Items such as condenser coils are often installed in walls of the cabinets and these coils are also easily damaged by acts of nature.
Gaps at the connection points of cabinet panels and access doors often result in air leaking into or out of the unit. This leakage can result in a substantial energy loss. Access doors are difficult to seal due to the differential pressures created by the circulating air inside the unit. Fastening devices for these doors often bend, break or become lost.
These cabinets are also sources of energy loss for the building due to their relatively low insulation relative to the building roof or walls. Because of the large amount of cabinet surface area exposed to the outdoor temperatures, heat loss through the cabinet can be substantial.
The enclosure is specifically designed to support and contain the internal equipment using a utilitarian approach. Aesthetics and conformance to the building architecture is generally not a consideration. For example, units placed on the roof of a Gothic style building or a modernistic building would have the same style. Architects have been known to refer to the roof mounted mechanical equipment as “roof warts” to denote their less than pleasing appearance. Therefore many buildings do not use roof mounted equipment because of the poor aesthetics that results.
To address the aesthetic issues, architects often design elaborate screening systems that may consist of extended wall parapets, fences mounted on the roof, and similar enclosed structures designed to conceal the equipment enclosures from view. However, these aesthetic measures add significant cost to the building, impair roof maintenance, and can reduce the performance and efficiency of the mechanical equipment. Walls, parapets and other barriers often cause eddy currents on the roof that limit the proper exhaust or intake of environmental air.